This application claims the priority of European Patent Application No. 97 120 547.1, filed Nov. 24, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a process for the cold forming of hollow workpieces with a circular cross section from workpiece blanks onto which, from the outside and by means of at least one forming tool in the shape of a roller, pressure or oscillation sequences are executed, in the course of which the workpiece, in relation to the roller, performs in the longitudinal axis a forward feed and is rotated. The invention also relates to an arrangement for the realization of the process.
Conventionally, for example, it is known to use press roll processes or impact roll processes for the cold forming of hollow pieces of such a kind.
During the press rolling, press rollers have a radial effect on a workpiece, which for example is arranged at the end of a spindle which is equipped with a matrix. As a result, the workpiece is rotated by the axially driven spindle and the press cylinders are pressed radially to the surface of the workpiece. Through an axial shift of the press cylinders in relation to the spindle and a radial infeed of the press cylinders, the desired shape of the workpiece is attained, in the course of which the internal shape is developed that corresponds to the matrix.
If hollow pieces are to be produced with an internal change of form, for example an internal toothing, a press roll process is known from German Patent document DE 4,218,092 for example, in which the thickness of the wall of the workpiece is reduced simultaneously with the change of form. Pressing and rolling are performed by means of a press cylinder, which is pressed onto the workpiece under high pressure and effects the forming. For the completion of this process, a high static pressure is necessary, which in turn requires a very stiff and heavy engine frame because the workpiece material and the workpiece blank must be rolled down by the press cylinder into the corresponding recess of the matrix. Depending on the internal shape that is to be created, this production process also causes strong vibrations, particularly in the areas where the wall thickness is thinnest, i.e., at those points where the internal wall of the hollow piece possesses grooves. For example, on one hand, this factor leads to the appearance of a great deal of wear and, on the other hand, leads in addition to a non-homogeneous external surface of the workpiece.
A cold forming process, which largely eliminates such disadvantages, is known for example from CH 658 006. This process is called an impact roll process, because in this case the force is not transferred to the workpiece statically by the press cylinders but instead by moving impact rollers, which are arranged on a roller head that rotates around its own axis on a rotary circular path. These impact rollers subsequently carry out abrupt, individual rolling on the cylindrical, hollow workpiece blank. As a result of this, the forces, in particular the static forces, can be kept at a lower level, which results in a smaller and lighter engine frame in comparison to the press roll devices. Now, a disadvantage of this approach can be, depending on the area of employment, that the large radius--conditional on the circular path of the impact roller--of the roller head, limits the kind of shapes that workpieces can have so that they can be machined with this process, for all practical purposes, to hollow bodies without externally projecting or respectively protruding flanges.
In order to reduce this problem, an impact roll process is now known from European Patent document EP 0 688 617, in which the impact roll processes are executed transversely to the axis of the workpiece. With this process, hollow pieces, which possess externally projecting shoulders or flanges, can now also be produced, as the thus arranged roller heads can be guided closer to the workpiece shoulder. Nevertheless, here in this case as well, there remains--as the result of the construction of the roller head in which the individual impact rollers run on bearings--a certain minimal space between the last section of the workpiece which can be reached by the impact rollers and its shoulder that cannot be machined.
The goal of the present invention is to provide a cold forming process with which such hollow pieces can be produced in a simple manner and which avoids the disadvantages and problems of the known processes, or at least reduces them.
This goal is achieved in accordance with the present invention by a process for the cold forming of hollow workpieces with a circular cross-section from workpiece blanks onto which, from the outside and by means of at least one forming tool in the shape of a roller, pressure or oscillation sequences are executed, in the course of which the workpiece, in relation to the roller, performs in the longitudinal axis a forward feed and is rotated on its longitudinal axis. The axes of the rollers are essentially guided parallel to the axis of the workpiece and are moved with an oscillating motion by an adjustable linear or curved oscillation.
It has been shown surprisingly that already the provision of a small reciprocating movement or respectively eccentricity of the rollers or roll cylinders significantly reduces the high static forces of the known press roll process, in the course of which, nevertheless, the good forming characteristics of the impact roll process are attained. In contrast to impact rollers, the rollers are not lifted off the workpiece, instead by preference they remain in contact with the surface of the tool. Simultaneously, the advantages of the press rolling can be utilized, such as for example the actuation of the press tools through the workpiece, as these are in contact with each other on their surfaces. Also of advantage is that the machine frame, as is known from impact roll machines, can be designed relatively small and light. Because, analogous to the press roll process, the roll tool is designed as one single roller and not one or more impact rollers run on bearings in the roller head, it is to the best advantage that with this process forming now can take place close to the externally projecting shoulder or flange, respectively, of a workpiece.
It is to the best advantage that analogously to the impact roll machines or systems, light machines can be realized which, in addition, require less space and can form workpieces that heretofore, because of the large radiuses of the impact rollers, were the exclusive domain of pure press roll machines or systems.
In accordance with the overall definition of the invention, the preferred designs of the process are further described herein.
An arrangement, in accordance with the present invention, for conducting the process includes a spindle for receiving a workpiece blank. Adjustable rollers with roll axes that are essentially placed parallel to the axis of the spindle are radially adjustable with respect to the workpiece. The device has means to perform a linear or circular oscillating, reciprocating movement, with adjustable oscillation of the axes of the rollers. Preferred designs of this device in accordance with the present invention are further described herein.